The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 100 42 243.8, filed on Aug. 28, 2000, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The invention relates to a process for monitoring web breaks in a machine for producing a material web, in particular a paper or cardboard web. It further relates to a machine for producing a material web, in particular a paper or cardboard web, in which such a monitoring of web breaks is embodied.
2. Discussion of Background Information
In multi-cylinder drying sections commonly used up to now, the paper web is guided over several steam-heated cylinders or over an arrangement of several steam-heated cylinders and wire suction rolls in order to be dried; however, the use of at least one impingement dryer has been suggested for impinging the material web with a hot air and/or hot steam impingement (see, for example, DE 198 41 768.3).
Usually, in paper machines the detection of a web break occurs at several points in the machine running direction on the guidance side or drive side within the cylinder drying section. Such a web break detection is used to avoid an uncontrolled accumulation of paper in the drying section and a so-called wrapping of the cylinders. Each detection of a web break causes a striking off of the paper web and/or a raising of the pick-up roll.
One problem occurs when impingement dryers are used in that the drying wires may be damaged in the event of a web break.
The present invention provides a process and machine of the type mentioned at the outset which virtually eliminates the danger of such damage to the drying wire although several impingement dryers are used.
According to the invention, the process for monitoring for web breaks in a machine for producing a material web, in particular a paper or cardboard web, includes guiding the material web through at least one impingement dryer, monitoring the material web, viewed in a web travel direction, for web breaks in the region before the intake into the impingement dryer and/or in the region after the exit from the impingement dryer and/or within the impingement dryer, and at least partially deactivating the impingement dryer when a web break is detected.
In the exemplary embodiment, the material web is monitored for web breaks, viewed in the web travel direction, preferably directly before the intake into the impingement dryer and/or directly after the exit from the impingement dryer and/or between several impingement dryers.
In a preferred practical embodiment according to the invention, the material web is monitored for a web break at least essentially over the entire width. Such a width-wide monitoring can also detect when parts of the web are missing only so that even a sporadic overheating of the drying wires is avoided as well.
In certain cases, however, it may be sufficient to monitor the material web for web breaks only on one or both lateral web edges. Thus, a monitor of the web edges on the guidance side and the driving side is fundamentally conceivable as well.
Generally, each impingement dryer is provided with at least one impingement hood. When a web break is detected, preferably at least one of the impingement hoods is deactivated corresponding to the respective impingement dryer.
In order to deactivate a respective impingement dryer, this dryer is reversed from a normal operational state in which the material web is preferably impinged by a hot air impingement and/or a hot steam impingement to a web break operational state in which only the internal hot air and/or hot steam circulation occurs.
Alternatively or additionally, for the purpose of deactivating the impingement hood, the burner assigned to it can be reversed to minimum capacity.
Alternatively or additionally, it is possible for deactivating a respective impingement hood to transfer this hood away from the normal production line into a transfer line.
After a web break, the deactivation of the impingement dryer should occur within about 20 seconds, preferably within about 10 seconds so that, even at an air temperature of about 300-500xc2x0 C., no overheating of the drying wires is caused.
According to a useful practical embodiment of the process according to the invention, when a web break is detected, in addition to the at least partial deactivation of the impingement dryer, at least one pick-up point is simultaneously opened as well, which is provided in the web travel direction before the impingement dryer and/or before and/or in the press section. This should occur within about 5 seconds, preferably less than about 2 seconds, after a web bread occurred.
Additionally, it is useful in certain cases for at least a partial deactivation of the impingement dryer to simultaneously cause the material web and/or paper web to be stricken off as well when a web break is detected.
According to a preferred practical embodiment, the material web is monitored for web breaks at least at one point by at least one sensor. Here, the use of most different types of sensors is conceivable. Advantageously, at least one optical sensor is used. In particular, a respective web break can be determined by color recognition or by image evaluation when a camera is used.
In certain cases, it is advantageous for at least one sensor to be directed to the material web, preferably directly after the respective impingement hood.
In the exemplary embodiment, the sensor can be directed towards the material web in a region in which the web is still positioned on a drying wire guided through the respective impingement dryer.
For example, it is also possible to direct the sensor to the material web in a region in which this web is positioned on the drying wire of a suctioned roll provided subsequent to the impingement dryer. This suctioned roll can be a suction roll or a so-called xe2x80x9cDuoStabi-roll,xe2x80x9d for example.
The drying wires are preferably made from plastic with the maximum allowable temperature being between about 100 and 300xc2x0 C. However, no damages should occur at temperatures between about 300 and 500xc2x0 C. on the drying wires during the deactivation of the impingement dryer.
However, it is also conceivable, to direct the sensor to the material web in the region of the first drying cylinder subsequent to the impingement dryer, with the material web being exposed after passing a previous wire and prior to the intake into another wire, with the sensor being directed towards the web section exposed. Therefore, the sensor can be directed towards the first cylinder after the impingement dryer when a group change occurs at this cylinder, thus resulting in a position at which the paper web is exposed.
In certain cases it can also be advantageous for the material web to be monitored in the region of a suctioned roll following the impingement dryer or one of the large suctioned rolls of the impingement dryer by monitoring the vacuum of this suctioned roll. As soon as the roll is no longer covered by the material web, particularly a paper web, the vacuum reduces considerably. For example, the suctioned roll can be a suction roll or a so-called xe2x80x9cDuoStabi-rollxe2x80x9d as well. Here, the suctioned roll is preferably provided inside of the first cylinder group subsequent to the impingement dryer. In particular, it can be provided before a detachment doctor, viewed in the web travel direction. In particular, it can be a the first suctioned roll subsequent to the impingement dryer.
The suctioned rolls to be monitored can also be the large suction rolls on which the impingement hoods are mounted.
According to a preferred useful embodiment of the process according to the invention, the material web is monitored for web breaks in the area of the impingement dryer positioned between a press section and a cylinder drying section of a machine for producing a material web.
In certain cases, it can be also advantageous to monitor the material web for web breaks in the area of the impingement dryer provided inside of a cylinder drying section of a machine for producing a material web.
For example, the material web can be monitored for web breaks in the region of an impingement dryer with the material web being guided at least partially along at least one straight or slightly bent and/or at least one, in particular larger, support roll, preferably suctioned.
The instant invention is also directed to a machine for producing a material web, in particular a paper or cardboard web, with at least one impingement dryer through which the material web is guided, a device for monitoring the material web for web breaks, viewed in the web travel direction, in a region before an intake into the impingement dryer and/or in the region after the exit from the impingement dryer, and a device for at least partially deactivating the impingement dryer when a web break is detected.
The device monitoring web breaks preferably include at least one sensor in order to monitor the material web for web breaks at least at one point using at least one such sensor.
In a useful practical embodiment of the machine according to the invention, the device for monitoring for web breaks and/or the device for deactivation include at least one electronic control.
This invention is particularly suitable in machines in which the material web is guided through the press nip(s) in the press section together with a belt in the form of a pressing felt or a transfer belt on both sides.
This invention is recommended at high machine speeds of above about 1100 m/min as well.
The present invention is directed to a process for monitoring web breaks in a machine for producing a material web that includes at least one impingement dryer. The process includes guiding the material web through the at least one impingement dryer, monitoring the material web for web breaks in at least one of a region, viewed in a web travel direction, before an intake into the at least one impingement dryer, after an exit from the at least one impingement dryer and within the at least one impingement dryer, and at least partially deactivating the at least one impingement dryer when a web break is detected.
According to a feature of the instant invention, the material web can include one of a paper and cardboard web.
Further, the at least one impingement dryer can include a plurality of impingement dryers, and the monitoring for web breaks may occur at least one of before an intake into one of the plurality of impingement dryers, directly after the exit from the one of the plurality of impingement dryers, and between successively arranged impingement dryers.
In accordance with another feature of the invention, the monitoring for web breaks can occur at least essentially over an entire width of the material web.
The monitoring for web breaks can occur along at least one lateral edge of the material web. Further, monitoring for web breaks may occur only along one edge of the material web. Also, monitoring for web breaks can occur along both lateral edges of the material web.
Moreover, at least one impingement dryer may include at least one impingement hood, and, when a web break is detected, the at least one impingement hood can be deactivated. The deactivation of the at least one impingement hood may include reversing operational states of the at least one impingement hood from a normal operational state, in which the material web is impinged with at least one of hot air and hot steam, to a web break operational state, in which the material web is impinged with at least one of hood-internal hot air and hot steam impingement occur. In the web break operational state, the material web can be impinged with only at least one of hood-internal hot air and hot steam. Further, the deactivating of the at least one impingement hood can include switching a burner assigned to the at least one impingement hood to minimum capacity. Further still, the deactivating of the impingement hood can include transferring the hood from a normal web travel line into a web transfer position.
The deactivation of the at least one impingement dryer can occur within about 20 seconds after the web break. Further, the deactivation of the at least one impingement dryer occurs within about 10 seconds after the web break.
When a web break is detected, the process can further include opening at least one pickup point located before the impingement dryer.
Further, when a web break is detected, the process can further include opening at least one pickup point is located at least one of before and in a press section.
When a web break is detected, the process may further include simultaneously striking off the material web.
The monitoring of the material web for web breaks may include positioning a sensor at least at one point and detecting the passage of the material web with the at least one sensor.
The monitoring of the material web for web breaks can include at least one of monitoring the material web with at least one optical sensor and at least one camera. Further, the web break may be detected by color recognition. Also, the web break can be detected by image evaluation.
Moreover, the at least one impingement dryer can include at least one impingement hood, and at least one sensor can be directed toward the material web at a location directly after the at least one impingement hood. A drying wire can be arranged to guide the material web through the at least one impingement dryer, and the at least one sensor can be directed toward a region of the material web which is positioned on the drying wire. Further, a drying wire may be arranged to guide the material web through the at least one impingement dryer and over a suctioned roll positioned after the at least one impingement dryer, and the at least one sensor can be directed toward a region of the material web which is positioned on the drying wire where it is guided over the suctioned roll. The machine can include a first drying wire and a second drying wire, and a drying cylinder can be arranged after the at least one impingement dryer to transfer the material web from the first drying wire to the second drying wire, and the at least one sensor may be directed toward a location where the material web is supported by the drying cylinder and between the first and second drying wires.
The at least one impingement dryer can include a suctioned roll and a suction roll can be arranged after the at least one impingement dryer, and the web breaks may be monitored by monitoring a vacuum of at least one of the suctioned roll and the suction roll. The suction roll can be located in of a first cylinder group located after the at least one impingement dryer. The suction roll can be located before a detachment doctor.
According to still another feature of the invention, the machine may include a press section and a cylinder drying section, and the monitoring for web breaks can occur in a region of the at least one impingement dryer positioned between the press section and the cylinder drying section.
In accordance with a further feature of the present invention, the machine may include a cylinder drying section, and the monitoring for web breaks can occur in a region of the at least one impingement dryer located in the cylinder drying section.
The at least one impingement dryer may include a guide path, which is at least one of a straight and slightly bent, on which the material web is at least partially guided, and the monitoring for web breaks can occur in a region of the at least one impingement dryer. The machine may include another impingement dryer including a suctioned support roll, and the monitoring for web breaks can further occur in a region of the suctioned support roll.
The machine can include another impingement dryer including a suctioned support roll, and the monitoring for web breaks can occur in a region of the suctioned support roll.
The present invention is directed to an apparatus for producing a material web. The apparatus includes at least one impingement dryer arranged so that the material web is guided through the at least one impingement dryer, monitoring device positioned to detect web breaks of the material web, the monitoring device being positioned in a region at least one of before an intake into the at least one impingement dryer, after an exit from the at least one impingement dryer, and within the at least one impingement dryer, and deactivating device arranged to at least partially deactivate the at least one impingement dryer when a web break is detected.
According to a feature of the invention, the material web can include one of a paper and cardboard web.
The at least one impingement dryer can include a plurality of impingement dryers, and the monitoring device may be positioned at least one of directly before an intake into one of the plurality of impingement dryers, directly after an exit from the one impingement dryer, and between successively arranged impingement dryers.
The monitoring device can be structured to detect web breaks at least essentially over an entire width of the material web.
Further, the monitoring device can be structured to detect web breaks along at least one lateral edge of the material web. The monitoring device may be structured to detect web breaks along only one lateral edge of the material web. The monitoring device can be structured to detect web breaks along both lateral edges of the material web.
Moreover, the at least one impingement dryer can include at least one impingement hood, which is structured to be deactivated upon detection of a web break. The at least one impingement hood can be structured to be reversible from a normal operational state, in which the material web is impinged by at least one of hot air and hot steam, to a web break operational state, in which the material web is impinged with at least one hot air and/or hot steam contained within the hood. Further, the at least one impingement hood can include a burner structured to be switchable to a minimum capacity when a web break.
The at least one impingement hood may be structured to be movable between a normal web travel line and a web transfer position.
Further, the apparatus can include an openable pick-up point located before the at least one impingement dryer, the openable pick-up point may be structured to open upon detection of a web break.
The apparatus can also include a device for striking off the material web upon detection of a web break.
In accordance with another feature of the instant invention, the monitoring device may include at least one sensor arranged to monitor the material web for web breaks.
According to still another feature of the invention, the monitoring device can include at least one of at least one optical sensor and at least one camera.
In accordance with a further feature of the present invention, the monitoring device may detect web breaks by at least one of color recognition and image analysis.
According to the invention, the at least one impingement dryer can include at least one impingement hood, and the monitoring device can include at least one sensor directed toward the material web subsequent to respective the at least one impingement hood. A drying wire may be arranged to guide the material web through the at least one impingement dryer. The monitoring device can include at least one sensor directed toward a location where material web it supported by the drying wire. Further, a drying wire and a suctioned roll can be arranged subsequent to the at least one impingement dryer. The at least one sensor can be directed toward a location where the material web is supported on the drying wire and on the suctioned roll. A drying wire can be arranged to guide the material web through the at least one impingement dryer, and the drying wire can be made of plastic with a maximum allowed temperature between about 100xc2x0 C. and 200xc2x0 C. Moreover, a first drying wire and a second drying wire, and a drying cylinder arranged after the at least one impingement dryer can be provided to transfer the material web from the first drying wire to the second drying wire. The at least one sensor can be directed toward a location where the material web is supported by the drying cylinder and between the first and second drying wires.
A suctioned roll can be positioned subsequent to the at least one impingement dryer. The monitored device can monitor a vacuum of the suctioned roll. The suctioned roll can be located inside a first cylinder group subsequent to the at least one impingement dryer. Further, the suctioned roll may be located before a detachment doctor.
According to a still further feature of the invention, the apparatus can include a press section and a cylinder drying section. The at least one impingement dryer can be located between the press section and the cylinder drying section, and the material web may be monitored for web breaks in a region of the at least one impingement dryer. The material web can be monitored for web breaks in a region of the at least one impingement dryer located within the cylinder drying section.
In accordance with another feature of the present invention, the at least one impingement dryer can include a guide path, which is at least one of a straight and slightly bent, on which the material web is at least partially guided, and web breaks may be monitored in a region of the at least one impingement dryer. Further, another impingement dryer can be provided that includes a suctioned support roll, and web breaks may be also monitored in a region of the suctioned support roll.
Further, another impingement dryer can be included that has a suctioned support roll, and web breaks can be monitored in a region of the suctioned support roll.
At least one of the monitoring device and the deactivation device can include at least one electronic control.
In accordance with still yet another feature of the present invention, two belts may be arranged to form a press nip, through which the material web is guided. Each of the two belts can be formed by one of a press felt and transfer belt.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.